Radio signaling system



RADIO S IGNALI NG SYSTEM INVENTOR GASTON ADELm MATmsu ORNEY Jan. 9, 1934, G. A. MATHIEU 1,942,561

RADIO SIGNALING SYSTEM v Filed ct. 25, 1928 s sheets-sheet 2 ENTOR A ADEUN MATHIEU ATTORNEY Patented Jan. 9'?, 1934 Gaston Adeiin Mathieu, London, England, assigner to Radio Corporation of America, a corporation of Delaware Application Gctober 25, 1928, Serial No. 314,885,

in Great Britain November 9, 1927 13 Claims.

This invention relates to radio andthe like high frequency receiving systems, and more particularly to multiple heterodyne ,receivers-i e. receivers incorporating a plurality of heterodynes-suitable for use in receiving continuous waves modulated at a plurality of frequencies or frequency ranges or any combination thereof for the purpose of providing a plurality of communication channels. y

In receivers comprising a plurality of heterodynes, and involving the use of band ilter amplifiers required for the simultaneous amplification of several frequencies tuning becomes a matter of considerable diculty, owing to the extreme degree of accuracy to which the local oscillators must be adjusted and owing to thenecessity of their frequencies maintaining a fixed relation-- ship, in order that the signal frequencies may be maintained centered on the `band filter amplifiers.

According to this invention a multiple heterodyne receiver comprises aplurality of heterodynes whereby, for correct reception, the same frequency is obtained at different parts of the receiver, means for feeding the said frequencies into a common control circuit, and means for adjusting one or more of said heterodynes, whereby azero or nil beat may be obtained in said common control circuit.

The invention is illustrated in the accompanying drawings, in which,

Fig. 1 shows schematically one form of receiver suitable for use to receive a carrier Wave modulated by three different signals, two of the modulations being telegraph modulations, and the third a telephone modulation; and,

Fig. 2 illustrates coupling apparatus utilized in Fig. 1; and,

Fig. 3 is a modification of the receiver illustrated in Fig. l.

It is to be understood, of course, that the invention is not limited to the particular applications illustrated and that the numerical values given in the following description are only by way of example.

4say 400 and 2400 cycles), a 7000 cycle telegraph -channel, and a 9000 cycle telegraph channel,

(Cl. Z-9) modulated upon a carrier wave of 20000 kilocycles, and it is assumed that the only wave bands radiated by the transmitter are:

(a) The carrier- 20,000 kilocycles.

(b) The telephone band, 20,000 kilocycles i the telephone frequency band.

(c) The rst telegraph band, 20,000 kilocycles i 7,000 cycles.

(d)l The second telegraph band, 20,000 kilocycles i- 9000 cycles.

Referring to Fig. 1 of the accompanying drawings, allA the frequencies are received upon an aerial lN and passed through a sharply tuned high frequency circuit T Whose cut-off is such that any wave whose frequency is more than 180,000 cycles greater than the carrier frequency (20,000, kilocycles) is eliminated. The modulated carrier from the output side of the tuned circuit is now changed to a modulated carrier of,180,000 cycles, by Vmeans of a firstv heterodyne H1, supplying 19,820 kilocycles, and modulated -valves Ml,- .the new modulat-ed carrier. being then amplified in a multi-stage filter amplier, A1 having a sharp loWerfcut-oif at 170,000 cycles, and a sharp upper cut-off at 190,000cycles, 'and so designed as to avoid anyrectification. v

The last stage of this amplier comprises coupling valves CVl, CVZ, Whose grid-anode capacities are Very carefully neutralized, and which are associated with sharply tuned circuits, Whereby the band of frequencies occupied by the telephone channel (which band lies in the middle of the whole band of the amplifier) is separated out from the said Whole band of the amplifier.

This frequency selective apparatus is illustrated in conventional diagrammatic form in Fig. 2 of the drawings which is self-explanatory. In Fig. 2, A represents the output of cut-off A. (Fig. 1) B represents the output of CVZ (Fig. 1) and C represents the output of CVl (Fig. 1). The Whole frequency band of 170,000-190,000 cycles is fed in at A and fed out at B (see Fig. 2), the central teleplicneband being fed out at C whence it is passed through a filter F1 (see Fig. 1) Whose cut-olf points are arranged to pass only those frequencies covered by the telephone modulated carrier. It is then rectified and amplified in a direct current amplifier D1, passed through an automatic` gain regulator, such as that described in my copending U. S.application,`Serial No. 239,843, filed Dec. 14, 192'?, and indicated at AGC and A2, re-amplied at A3 and transmitted down a land-line or utilized in any other way. It will be noted that the telephone channel is separated out prior torectification, an arrangement which, in conjunction with the telephone iilter, substantially eliminates the keyclicks of the telegraph transmission from the telephone channel.

The output from line B (see Fig. 2) is subjected to the Vaction of a second heterodyne H2 supplying 150,000 cycles (see Fig. 1) and modulators M2, whereby the carrier frequency is changed to a frequency of 30,000 cycles and this new carrier is eliminated by a filter F2 having'an infinite impedance to 30,000 cycles per second. This carrier elimination is efiectedf'or the' following reasons:-

1. The carrier wave is vmuch more powerful than any of the modulating waves and consequently any attempt to secure a further large amplification of all the modulated Waves separately or as a unit without suppressing the carrier, would prove a Very diflicult matterif saturation and rectification are to be carefully avoided as is thefcase.

2. Because Vin the use of short waves it Ihas been found `that with armodulation of '5000 cycles and upwards, the difference in time for fading for the carrier and the two side waves begins to be sufficiently marked to make use of -this phenomenon considerably to reduce the consequence of fading, first by Ausing the side waves separately and secondly by eliminatingthe variable carrier` and resupplying itvl'ater at a constant amplitude.

The modulated signals having the .carrier suppressed are now passed through a pair of parallel filters F3, F4 Ione of which is a high pass and the other a low pass filter, designed to separate the upper and-lower modulation side -bands land to attenuate strongly the telephone-frequencies. The low pass lter admits only frequencies below26,00'0 cycles and the highpass ltcradmits only frequencies `above l341,000'cycles per second. The side bands are thus separated'in order to obtain the advantage 'of the frequently observed time differences in fading which occurs between them. It is obvious that the high and lowpass filters can be replaced by suitable band lters.

The outputs from the filters F3, TFi are now passed through multi-stage band filter amplifiers A4,A5, designed each toadmit arfrequency band'4000 cycles wide on a ycentral frequency in one case 8,000cycles'above, and inthe other 8,000 cycles below 30,000 cycles, (3,000 cycles is of course, the central frequency between the two telegraph frequencies). The outputs from these band filter amplicrs operate into remodulators R1, R2, whereby the suppressed carrier is resupplied at constant amplitude by a local-"gen-f erator G operating through coupling valves CV3, CVl. This local generator, and the second heterodyne whereby a carrier frequency of 30,000

f cycles was rst obtained, must be of as constant frequency and as pure'and free from vharmonics as possible. Preferably each is Igoverned by means of a known neon tube indicating wavemeter or similar device (indicated at'Wl andWZ) whereby their frequencies may be adjusted-'and maintained within cycles of the vrequired value-a degree of I accuracy which is amply sufcient.

-The outputs from the remodulators, 'which `deal eachfwith one side band, are now passed through `combine their effect into the same limiting Valve pairs F5, F6, F5', F6', of parallel filters, one filter of each pair being adapted to pass 7000 cycles i 500 cycles (the allowance made for Variation in the original radio-transmitted carrier), the other being designed to pass 9000 cycles i' 500 cycles. The now separated telegraph frequencies are rectified at D2, D3 and D4, D5, and the direct current components of the corresponding frequencies passed through limiting Valves L1 V1, L2 V2, and suitable telegraph bridges B1 B2 to be retransmitted in any desired way.

It is also ipossible to .join the "direct current output component of the upper and lower side bands of each of the telegraph channels and to 00 and telegraph bridges instead of recording them I separately.

In the case where the time constant is found tobe slightly'different for the signals originatingf'f'rom the output of the upper and lower side bands, the required correction of time can be obtained by the use of a delay circuit introduced either in the high or the low frequency of one of the telegraph detectors. Such delay circuits are indicated at The local generator'G'is also'arranged to `feed (preferably through-couplingva1ve CV5) a detector controlling Icircuit M3 (preferablyof the push-pull type) whose inputcircuit is 'also fed as shown from -one or all of the Vtrap circuits involved in the construction of Ythe vfilter F2 -designed for the suppression of fthe 30,000 cycle carrier. y

It will be seen that the simultaneous action on thersaid `controllingdetector M3 of fthe vcarrier, and the 30,000 cycle wave ofthe llocal generator, will produce a beat notein the output of the detector, the said beat being vzerowhenithe original carrier is -changed exactly to 30,000 -cycles, Aby the action of -the firstfandsecond-heterodynes. This beat is amplified'at A6 and-'fed to a loudspeakeror indicating instrumentZ.

In practicethe localgenerator G lan'd'thesecond Aheterodynel+12 maybeadjusted to be usubstantially constant and the latter can be maintained adjusted to thecorrect Vvwave vlengthfto produce 'a beatof '30,'000-cycles, so long as'the first 'heterodyne Ychanges the original carrierto 180,000 cycles-#the `middle frequency -of the `first band amplier-so that adjustment is-reduced to thatef the first heterodyne.

It is obvious v'that any variation from the original adjustment will alter `the Zero beat vnote lat A6 into an acoustic 4one `(due either-to variati'on in thelfrequencynof the carrier-ati the trans- 130 mitting station or to the variation Sof the heterodynesr of the receivingl'station) -Ywhosefrequency will indicate in cyclesthe vlamount'fofithe variation.

To prevent-the :speech frequency appearing .inY 135 the output :ofvnthei-said controlling'valve, allowpassfilter 'with asharpcut-off of 500 cyclesiis incorporated in connection with M3.

The cutputof this'filter maybe amplified, :as stated above, by the low frequency amplifier ,A6140 workingwinto aloud speaker which will onlylbe silent` for thea-zero 'point `of adjustment. A'Mere-- over, if desired,.ther.e .maybe inserted Iinthe output circuitof `the amplifier vA6 Asensitive relays tuned to say 250, 350 and 450 cycles, and'adapt-45 ed to light'lampsf of different colors. Such relays are 'indicated at l, -2 and 3 in -Fig. 3, :the lamps being lindicated. bynumerals 4,: l5 and 6.

In a modificationof theabove described arrangement, :a harmonic of the generator Gris; utiv150 lized as the second heterodyne H2, and thereby the installation is renderedstill more convenient to control and satisfactory to use. For example, if the middle band frequency of the amplifier Al is chosen at 181,998 cycles, andthe carrierfrequency to be suppressed at F2 and 4re-supplied at R1, R2 is 30,333 cycles, the seventh harmonic of the frequency generated at G (i. e. 212,331 cycles) will be the correct frequency to be supplied at M2.

This arrangement is also shown in Fig. 3 Where G is the harmonic generator and '7 and 8 are filters for passing respectively 30,333vcyclesjand 181,998 cycles. l l

Where a plurality of receivers 'in' accordance with this invention are to be located close' to one another, for example, in the same room-a preferred arrangement is to employ a common master generator (G) for al1 the receivers a harmonic of the output of the said generator being yemployed as a master second heterodyne 4(H2) for all the receivers. This arrangement-avoids much interference which might otherwise occur from undesired beats.

, A harmonic frequency may be obtained from the generator G in any desired manner. jThe following method has, however,been found suitable in practice:- i

The fundamental frequency is generated by a valve circuit and flows in an oscillatory circuit comprising a condenser shunted by an inductance.

Owing to the fact that the impedance `of the condenser to harmonic frequency is much less than the impedance of the inductance, a larger current of the harmonic frequency will flow in the condenser branch, and by coupling a coil to a small inductance in this branch, the current of harmonic frequency can be obtained and applied in a tuned amplifier to raise its amplitude to a suitable value.

It will be seen that controlling arrangements as herein described secure:-

(l) A Very simple means of tuning a multiplex receiver which would otherwise be intricate.

(2) An instantaneous indicator for al1 variation occurring or needed at the receiver.

It will be realized that the controlling device (providing the local generator is free from undesired harmonics) cannot introduce any perturbation in the telephone channel working on 180,000 plus or minus 2500 cycles.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:-

1. The method of signaling utilizing the reception of a carrier wave modulated by a plurality of signals, which includes reducing the frequency of the carrier of all of the signals, separating the side bands of the reduced carrier, detecting side bands of the reduced carrier caused by one of the signals, and still further reducing the carrier frequency of other of said signals, filtering out the last utilized carrier, amplifying the side bands of said last utilized carrier and resupplying the carrier to the amplified side bands.

2. The method of signaling utilizing the reception of a carrier Wave modulated by a plurality of signals, which includes reducing the frequency of the carrier of all of the signals, separating the side bands of the reduced carrier, detecting side bands of the reduced carrier caused by one of the signals, and still further reducing the carrier frequency of other of said signals, isolating the last utilized carrier, amplifying the side bands of said lastutilized carrier, generating ,a constant amplitude(carriensupplying the generated carrier to thel amplified side bands-and combining the, generated carrier and the isolated carrier.

3. `The method of signaling utilizing the reception of a carrier modulated by a plurality of signals' which includes filtering the received carrier so' as to pass substantially the frequencies covered by the modulated carrier, reducing the carrier frequency, separating a band of frequencies caused by one Vof the signals from the reduced modulated carrier, further reducing the carrier frequency of the other signals, shunting out the further reduced carrier, resupplying a carrier to the side bands and combining the shunted out carrier and the resupplied carrier. 4. In combination, in a radio receiver adapted for the carrier wave modulated by a plurality of signals, which includes means 'forredurcing the frequency ofthe carrier of all of the signals, means for separating the side bands of the reduced carrier, means for detecting side bands of the reduced carrier caused by one of the sig- Iials, means for still further reducing the carrier frequency of other of said signals, means for eliminating the last utilized carrier, means for amplifying side bands of said last utilized carrier and means for resupplying a carrier to the amplifiedV side bands.

5. In rcombinationjn a radio receiver adapted for receiving a carrier modulated by a plurality of signals, means for reducing the frequency of the carrier of all the signals, means for separating the sidebands of the reduced carrier, means for detecting side bands of the reduced carrier caused by one of the signals, and means for still further reducing the carrier frequency of other of said signals, means for isolating the last utilized carrier, means for amplifying the side bands of said last utilized carrier, `a generator for generating a constant amplitude carrier, means for supplying the generated carrier to the amplified side bands, and means for beating together the generated and the isolated carrier.

6. In combination, a filter for passing substantially all of the frequencies covered by modulating a carrier by a plurality of signals, heterodyning means for reducing the carrier frequency, means for separating a band of frequencies caused by one of the signals fromj the reduced modulated carrier, other heterodyning means for further reducing the carrier frequency of the other signals, means for shunting out the further reduced carrier, means for separating and amplifying the side bands of the carrier which has been shunted out, means for generating a carrier, and means for combining the generated carrier and the carrier which has been shunted out to produce a beat note.

7. The method of signaling, utilizing the reception of a carrier wave modulated by a plurality of signals, which includes reducing the frequency of thecarrier of all of the signals; separating out certain of the side bands of the reduced carrier and detecting said side bands for deriving therefrom certain of the signals and still further reducing the carrier frequency of the other of said signals.

8. In a system for receiving a carrier Wave modulated by a plurality of frequency bands, means for receiving said carrier wave, a band filtering llO modulated carrier frequency to 'la predetermined 'value so that -a lcer-tain -oe of -`said 'frequency bands -Will beapproximately in *thef I'niddlefof lthe band covered-by the'said reduce'dimodulated carrier,-"rr1eans=forltering out and util-""ngthes'aid modulated band,- va' secondheterodyiie ifor' changing thel frequency 'of 'the vvremaining'ipart-of said reduced modulated carrier, means vfor l'teiiriig outfthis further ifeducedcarrier', "ansffor diy-iding the remaining energy E-nto LAcori/stitielerit Lsid'e bands, means yfor amplifying "each fof said sile bands, meansfcr vresupplyingfsaid last mentioned 'carrier Wav@ and means l fOr utilizing the neg'y ineach of -said amplified sideba'nds.

9. Means forrec'eiV-ingaicarierinodlatedby a plurality f signalfrequencies including, -reans for producing and combining Va plurality of beat frequencies with said; 'carrier -fequ'n`cy,fsai beat frequencies being such as -to yproduce the fsaine carrier frequency Ain different Y"parts V*of the Ifile'- ceiving means, means ferlbea'tingthe last-named frequencies, rand-Irieansfor indicating the resultantbeatnote. y

1-0. 'A' receiver for receiving la'fcarr'ier l frequency modulated by "a `pl'iality of signal `lfreqiiericies comprising, li'ete'rodyne itmeans lier reducing"- l'said Acarrier frequency, vmeans f for -ltr-ing fout y"said carrier, A means forI producing avv newpa'rrier 'of v a frequency equal to `the-ls'u'prnessedE carrier-251:0 'be supplied to the Wave resulting -fro'mv'fsaid -ltered carrier, 'and 'means for combi-ning `said-new carrier and said filtered 'carrie1"' whereby afresulting Zero beat noteindicates-ftlie *tune ofl--said receiver.

11. VReceiving means for demodul-'atingf'a carrier frequency Yon Whichhas been ysupe'r'po's"e'd"a-plu rality 4of signal vfrequencies including, L'lietero'- slfluitinglelfithecarrierafgenerator for producing cluding, ahindioatingdevice actuated Whenthe system, means-for reducing `said carrier'- frequency chiiecteizltol'Isaidi'filter circuit',a'linear amplifier connected to-*saidfL-reducing means', means for sepaliating one i ith'ef Esignal frequencies @from said hig'h frequenti" carrierfme'ans `for reducing the fieqlen'cy-oi -th "duced carrieitofproduce a 'new ca'- ierfmeans-fcr isolfatingthe newfcarrie'r, -filter ciruitsffori iite'ringe; out th'e remainings'ignalvfrequencies, a local frequency generator producing a vean-*ier frequency substantially similar -to 'the isolated -lrequency means forfcor'yxiibining *said locally @generated :carrier With -said=-signal 'frequencies to produce a plurality r`eisifle bands, meansifr-ltering out saidfisid'ebands, detecting meaiisi connectedWith'saidrltering means, utilizing -izircl'lits connected with Iflsaidf detecting A cir-` cuits, and means for combining said isolated carrier vfaridfsaid. locally generated carrier. to\produce albeat#notewhich indicates-the .tune Aof the receiver.

l GASTON 'ADELIN f MATHIEU. Y 

